Separation and recovery of perhalogenated fluorocarbons

ABSTRACT

PERHALOGENATED FLUOROCARBONS, E.G., PERFLUOROCARBONS AND/OR CHLOROFLUOROCARBONS, CONTAINED IN A MIXTURE TOGETHER WITH PARTIALLY HALOGENATED FLUOROHYDROCARBONS, E.G., CHLOROFLUOROHYDROCARBONS, ARE SEPARATED AND RECOVERED BY DEHYDROHALOGENATING SAID PARTIALLY HALOGENATED FLUOROHYDROCARBONS TO THE CORRESPONDING OLEFINS WHICH ARE THEN HALOGENATED TO PERHALOGENATED FLUOROCARBONS. THE RESULTANT MIXTURE IS THEN FRACTIONATED TO SEPARATE AND RECOVER THEPERHALOGENATED FLUOROCARBONS.

June 5, 1973 J. E. come 3,737,470

SEPARATION AND RECOVERY OF PERHALOGENATED FLUOROCARBONS Filed June 8,1970 4 TTOR/VEVS 3,737,470 SEPARATION AND RECOVERY F PERHALO- GENATEDFLUOROCARBONS John E. Cottle, Bartlesville, Okla., assigner to PhillipsPetroleum Company Filed June 8, 1970, Ser. No. 44,513 Int. Cl. C07c17/34, 19/08, 21/18 U.S. Cl. 260--653 7 Claims ABSTRACT OF THEDISCLOSURE Perhalogenated uorocarbons, e.g., pertluorocarbons and/orchlorouorocarbons, contained in a mixture together with partiallyhalogenated fluorohydrocarbons, eg., chlorouorohydrocarbons, areseparated and recovered by dehydrohalogenating said partiallyhalogenated luorohydrocarbons to the corresponding oleins which are thenhalogenated to perhalogenated uorocarbons. The resultant mixture is thenfractionated to separate and recover the perhalogenated uorocarbons.

This invention relates to the separation and recovery of perhalogenatediluorocarbons.

Herein and in the claims, unless otherwise specied, the termperhalogenated uorocarbons is employed generically to refer to compounds(a) which contain only uorine and carbon, and (b) also to compoundswhich contain only liuorine, carbon, and another halogen other thanuorine, e.g., chlorine; and the term partially halogenatedfluorohydrocarbons or the term halogenated lluorohydrocarbons refers tocompounds which contain only fluorine, carbon, hydrogen, and anotherhalogen other than duorine, eg., chlorine. For convenience, theinvention will be described herein with particular reference toperhalogenated uorocarbons .and halogenated uorohydrocarbons whereinchlorine is the halogen present other than luorine, for example,chlorofluorocarbons and chloroiiuorohydrocarbons, respectively. However,the invention is not so limited. Said other halogen can also be bromineor iodine.

The invention is applicable to mixtures of perhalogenated iluorocarbonsand halogenated liuorohydrocarbons obtained from any source. Saidmixtures are commonly obtained in processes for uorinating halogenatedhydrocarbons, eg., chlorinated hydrocarbons. One such process comprisesdirect fluorination using elemental iluorine. Another fluorinationprocess comprises using cobalt triiluoride. However, in recent yearsmore practical electrochemical fluorination processes have beendeveloped. The invention is particularly applicable to product mixturesobtained in electrochemical tluorination processes.

Due to the reactivity of the uorine and the other halogen present,e.g.,ch1orine, a considerable variety of products is produced in saidiluorination processes. Thus, a problem common to all of saidfluorination processes is the separation and recovery of the productsobtained therein. This problem is aggravated by the fact that in manyinstances the boiling points of some of said products are close, makingseparation by fractional distillation ditiicult.

The present invention provides a solution to the abovedescribedproblems. Broadly speaking, the present invention provides a combinationof steps wherein in a mixture containing perhalogenated uorocarbons,e.g., chlorofluorocarbons, together with partially halogenateduorohydrocarbons, e.g., chlorouorohydrocarbons, said partiallyhalogenated fluorohydrocarbons are lirst dehydrohalogenated to thecorresponding olens. Said oleiins Vare then halogenated toperhalogenated uorocarbons, and the resultant mixture is thenfractionated to separate andrecover said perhalogenated uorocarbons.

" United States Patent O An object of this invention is to provide amethod for the separation of, and the recovery of, perhalogenatedfluorocarbon compounds present in mixtures containing the same togetherwith halogenated fluorohydrocarbon compounds. Another object of thisinvention is to provide an improved electrochemical uorination process.Still another object of this invention is to provide an improved processfor the separation of, and the recovery of, valuable perhalogenatedluorocarbon compounds present in a cell effluent stream from anelectrochemical uorination process for the iluorination of1,2-dichloroethane. Other aspects, objects, and advantages of theinvention will be apparent to those skilled in the art in view of thisdisclosure.

Thus, according to the invention, there is provided a process for theseparation of, and the recovery of, perhalogenated fluorocarbonscontained in a mixture with halogenated uorohydrocarbons which contain ahalogen other than iluorine and at least some of which are capable ofbeing dehydrohalogenated to the corresponding olefin, which processcomprises, in combination, the steps of: (a) contacting said mixture ina dehydrohalogenation zone with a dehydrohalogenation agent anddehydrohalogenating said halogenated iiuorohydrocarbons to removetherefrom at least one atom of hydrogen and one atom of said halogenother than liuorine and produce a second mixture containing saidcorresponding olefins; (b) fractionating an effluent stream from saiddehydrohalogenation zone to recover an overhead stream comprising saidoleins, and a bottoms stream comprising perhalogenated uorocarbons; (c)passing said overhead stream from step (b) to a halogenation zone andtherein halogenating said olefins to perhalogenated uorocarbons; (d)fractionating an effluent stream from said halogenation zone to recoveran overhead stream comprising said perhalogenated fluorocarbons producedin said step (c) (e) combining said bottoms stream from step (b) andsaid overhead stream from step (d) to obtain a second mixture comprisingsaid perhalogenated uorocarbons present in said lirst mixture and saidperhalogenated uorocarbons produced in said step (c); and (f)fractionating said second mixture to separate and recover saidperhalogenated uorocarbons.

Further, according to the invention, there is provided in a process forthe iiuorination of a halogenated hydrocarbon feedstock wherein there isproduced a mixture of perhalogenated uorocarbons containing a halogenother than uorine and partially halogenated iiuorohydrocarbons alsocontaining said halogen other than tluorine, and wherein saidperhalogenated iiuorocarbons are recovered from said mixture, theimprovement comprising: (a) passing at least a portion of said mixtureto a dehydrohalogenation zone and therein dehydrohalogenating saidpartially halogenated uorohydrocarbons to remove therefrom at least oneatom of hydrogen and one atom of said halogen other than uorine andproduce a second mixture containing said corresponding olens; (b)fractionating an effluent stream from said dehydrohalogenation zone torecover an overhead stream comprising said oleiins, and a bottoms streamcomprising perhalogenated uorocarbons; (c) passing said overhead streamfrom step (b) to a halogenation zone and therein halogenating saidoleins to perhalogenated iiuorocarbons; (d) fractionating au effluentstream from said halogenation zone to recover an overhead streamcomprising said perhalogenated uorocarbons produced in said step (c);(e) combining said bottoms stream from step (b) and said overhead streamfrom step (d) to obtain a second mixture comprising said perhalogenateduorocarbons present in said rst mixture and said perhalogenateduorocarbons produced in step (c), and (f) fractionating said secondmixture to separate and recover 'said perhalogenated fluorocarbons.

A number of advantages are obtained or realized in the practice of theinvention. One important advantage is that the separation and recoveryof perhalogenated fluorocarbons is facilitated. Another importantadvantage is that the production of desired products can be increasedandthe production of undesired products decreased. For example, theinvention is particularly advantageous when it is desired to increasethe production of the desirable productl,1,2-trichloro-1,2,2-trifluoroethane. Mixtures of perhalogenatedliuorocarbons and partially halogenated fluorohydrocarbons containingsaid 1,l,2-trichlorol,2,2 trifluoroethane usually also containappreciable amounts of 1,2-dichloro-1,2,2-trifluoroethane. In thepractice of this invention said 1,2-dichloro-1,2,2-trifluoroethane isultimately converted to said desirable product1,1,2-trichloro-1,2,2-trifluoroethane, thus increasing the production ofsaid desirable product. Another important advantage is that theperhalogenated fluorocarbon products can be recovered in increasedpurity. For example, said desired product,1,1,2-trichloro-1,2,2,-triuoroethane boils at 47.6 C. In mixtures of thetype to which this invention relates there is usually also present asignificant amount of 1,2-dichloro-1,1-difluoroethane which boils at46.8 C. From a practical fractionation standpoint it is very diicult toseparate these two compounds. In the practice of this invention said1,2-dichloro-1,1-difluoroethane is ultimately converted tol,2,2,trichloro-l,lditiuoroethane, having a boiling point of 71.9 C.,which presents no particular problem in separation. Another importantadvantage is that more efficient electrochemical iuorination is obtainedby eliminating undesirable components from the stream or streamsrecycled through the electrochemical iluorination cell when the mixturebeing separated in accordance with the invention is obtained as a.product of electrochemical iiuorination. This provides the additionaladvantage of increased flexibility in the electrochemical fluorinationprocess in that operating parameters can be more readily adjusted tovary the ratio of desired products. Said advantages are illustratedfurther hereinafter in connection with the example.

The invention is applicable to mixtures of perhalofluorocarbons andhalogenated lluorohydrocarbons obtained from any source. The inventionis particularly applicable to such mixtures which are obtained as a celleffluent stream from an electrochemical fluorination process. Thus, theinvention is applicable to electrochemical fluorination processeswherein the feedstock is dissolved in the electrolyte. The invention isalso applicable to electrochemical fluorination process wherein thefeedstock is bubbled into the electrolyte through a porous anode. In apresently preferred electrochemical fluorination process, to which theinvention is particularly appliy cable, a current-conducting,essentially anhydrous, liquid hydrogen fluoride electrolyte iselectrolyzed in an electrolysis cell provided with a cathode and anonwetting porous anode (preferably porous carbon), and the feedstock isintroduced into the pores of said anode and uorinated within said pores.

Briefly, said preferred electrochemical fluorination process comprisespassing the feedstock to be fluorinated into the pores of a nonwettingporous anode, e.g., porous carbon, disposed in a current-conducting,essentially anhydrous, hydrogen fluoride electrolyte such as KF-ZHF.

' Said feedstock contacts the iluorinating species within the pressurebalance within the pores of the anode between the feedstock entering thepores and electrolyte attempting to enter said pores from another andopposing direction. Said feedstock flow rate can be within the range offrom 3 to 600 milliliters per minute per square centimeter of anodecross-sectional area, taken perpendicular to the direction of flow andexpressed in terms of gaseous volume calculated at standard conditions.Current densities, employed can be within the range of 30 to 1000,preferably 50 to 500, milliamps per square centimeter of anode geometricsurface area. Typical cell vvoltages employed can range from 4 to l2volts. Converted and unconverted products are withdrawn from the poresof the anode and the products recovered from a cell effluent stream.

Further details of said preferred electrochemical uorination process canbe found in U.S. Pat. 3,511,760, issued May 12, 1970, to H. M. Fox andF. N. Ruehlen.

As illustrated herein, the invention is particularly applicable tomixtures of aliphatic perhalouorocarbons and halogenatedfluorohydrocarbons containing 2 carbon atoms per molecule. However, theinvention is not limited to such mixtures. The invention is applicableto mixtures and the separation and recovery or perhalofluorocarbons andhalogenated fluorohydrocarbons containing more than 2 carbon atoms permolecule, eg., up to 4 carbon atoms per molecule, and higher.

The drawing is a diagrammatic ow sheet illustrating one presentlypreferred embodiment of the invention wherein a feedstock, e.g.,1,2-dichloroethane, is uorinated and the products obtained are separatedin accordance with the invention.

Referring now to the drawing, the invention will be more fullyexplained. By way of example, and not by way of limitation, theinvention will de described with particular reference to using1,2-dichloroethane as the fresh feedstock to an electrolytic cell. Thus,the typical operating conditions given herein in connection with usingsaid feedstock and separating the products obtained therefrom are not tobe construed as limiting on the invention. It will also be understoodthat many valves, pumps, control instruments, etc., not necessary forexplaining the invention have been omitted for the sake of brevity. Insaid drawing there is illustrated an electrolytic cell, denotedgenerally by the reference numeral 10, comprising a cell body 12 havingan anode 14 disposed therein. As here illustrated diagrammatically, saidanode in its simplest form comprises a cylinder of porous carbon havinga cavity 16 formed in the bottom thereof. Any suitable anode can beemployed in said cell. Examples of other suitable anodes can be found inU.S. Pat. 3,511,762, issued May 12, 1970, to W. V. Childs. A currentcollector 18 usually comprising a rod or hollow conduit of a metal suchas copper, is provided in intimate contact with the upper portion ofsaid anode 14 and is connected to the anode bus of the current supply.Preferably, the upper end of anode 14 extends above the electrolytelevel 20. However, it is within the scope of the invention for the topof said anode to be below said electrolyte level. A circular cathode 22,which can be a screen formed of a suitable metal, such as carbon steelor stainless steel, surrounds said anode 14 and is connected to thecathode bus of the current supply by a suitable lead Wire 24. Anysuitable source of current and connections thereto can be emlployed.

In the operation of the system illustrated, a feedstock such as1,2-dichloroethane is introduced into the cavity portion 16 of saidanode via conduits 26 and 28, travels upward through the pores of saidanode, and exits from the upper end of the anode above electrolyte level20. During passage through said anode at least a portion of thefeedstock is electrochemically fluorinated. Fluorinated productstogether with remaining unconverted feedstock, hydrogen, and possiblysome electrolyte vapors, are withdrawn from the space above theelectrolyte within cell 12 via conduit 30. During the introduction ofsaid feedstock an electric current in an amount suficient to supply thedesired operating current density at the anode is passed between theanode and the cathode.

The cell efuent stream in conduit 30 is passed into hydrogen and HFremoval zone 32. Said zone 32 can comprise any suitable means forremoving hydrogen and HF from the cell efliuent stream. For example,said cell efiiuent stream can first be cooled, by either'direct heatexchange or indirect `heat exchange, to a temperature which is near itsdew point but which is insufficient to cause any significantcondensation of the components thereof. As will be understood by thoseskilled in the art, said dew point will vary with the composition ofsaid effluent stream and the pressure thereon. Thus,- the temperature towhich said efliuent stream is cooled can vary widely. When1,2-dichloroethane is the charge stock to the electrochemicalfluorination cell, said dew point will usually be in the order of about115 to about 125 F. (4G-52 C.). Generally speaking, it is desirable tocool said effluent stream as nearly as practical to its dew pointwithout causing said condensation of the components thereof. In mostinstances said eflluent stream will be cooled to a temperature which iswithin about 3 to 10 F. (l to 5 C.) above said dew point. The cooledeffluent stream can then be compressed to a pressure of about 30p.s.i.a. and then chilled by refrigeration to a temperature of about 20F. (-29 C.) at a pressure of about 27 p.s.i.a. The chilled eiiluentstream can then be passed to a phase separation zone from which hydrogencan be removed, compressed, and said compressed hydrogen chilled bymeans of refrigeration to a temperature of about 100 F. (-73 C.) at apressure of about 80 p.s.i.a. Said chilled hydrogencontaining stream canthen be passed to a second phase separation zone from which hydrogen isvented. Liquid hydrogen iuoride can be returned from second phaseseparation zone to said tirst-mentioned phase separation zone. A streamof liquid hydrogen fluoride can be recycled from said rst phaseseparation zone to the electrolytic cell, if desired. A second liquidstream comprising the fluorinated products contained in the celleiiiuent stream can be withdrawn from the first phase separation zoneand passed to a stripping zone for the removal of trace amounts ofhydrogen fluoride which may remain therein. The abovedescribed methodfor the removal of hydrogen and HF from the cell efuent stream isdisclosed and claimed in copending application Ser. No. 44,041, filedJune 8, 1970, by R. O. Dunn, now U.S. Pat. 3,660,254 issued May 2, 1972.

The now essentially hydrogen-free and essentially HF- free efiiuentstream is removed from zone 32 via conduit 34 and passed into a firstdistillation zone comprising a first fractionation column 36 and asecond fractionation column 38. As indicated above, the invention isapplicable to mixtures of perhalogenated uorocarbons and halogenatedfluorohydrocarbons from any source. Thus, it is within the scope of theinvention to introduce such a mixture into the system from an outsidesource via conduit 40. Said rst fractionation column 36 can convenientlybe operated at a pressure of about 130 p.s.i.a., a top tower temperatureof about 145 F. (63 C.), and a bottom tower temperature of about 256 F(124 C.). An overhead stream comprising chloropentauoroethane and1-chloro-1,l,2,2tetrauoroethane, and possibly a small amount ofl,2-dichlorotetrauoroethane, is withdrawn from said fractionation column36 via conduit 42. If desired, said overhead stream in conduit 42 can befurther fractionated for the recovery of said chloropentauoroethane as aproduct of the process. If the mixture introduced into distillationcolumn 36 was obtained from an electrochemical iiuorination cell, the1chloro1,1,2,2tet raliuoroethane recovered from said Ifurtherfractionation of the stream in conduit 42 can be recycled to theelectrochemical iiuorination cell. A bottom stream comprising the majorportion of the cell eluent stream is withdrawn from fractionation column36 via conduit 44 and introduced into second fractionation column 38.Said second fractionation column 38 can conveniently be operated at apressure of about 170 p.s.i.a., a top tower temperature of about 120 F.(49 C.), and a bottom tower temperature of about 340 F. (171 C.). Abottom stream comprising unreacted 1,2-dichloroethane feedstock and thehigher boiling fluorinated products is withdrawn from said fractionationcolumn 38 via conduit 46. Such stream in conduit 46 can be removed fromthe'system via conduit 48 if desired. However, in those instances wherethe invention is `being practiced in connection with an electrochemicaliluorination process, said stream in conduit 46 will preferably bepassed to conduit 50 for recycle to the electrochemical iluorinationcell 12 as a portion of the feedstock thereto.

An overhead stream comprising perhalogenated iluorocarbons and partiallyhalogenated uorohydrocarbons having boiling points below approximatelyv50 C. is withdrawn from said second fractionation column 38V via conduit52 and passed via conduit 54 into dehydrohalogenation zone 56. Ifdesired, depending upon the composition thereof, a mixture ofperhalogenated iiuorocarbons and partially halogenatedfluorohydrocarbons can be introduced into the system via conduit 58,instead of, or in addition to, the stream from conduit 52, and thenintroduced via conduit 54 into said dehydrohalogenation zone 56.

Said dehydrohalogenation zone can comprise any suitable process andmeans known in the art for dehydrohalogenating materials capable ofbeing dehydrohalogenated, i.e., materials having a halogen atom on onecarbon atom and a hydrogen atom on an adjacent carbon atom. Any suitabledehydrohalogenation agent can be used in the practice of the invention.The alkaline dehydrohalogenating agents are preferred. However, it isWithin the scope of the invention to use the so-called acidicdehydrohalogenation agents. Examples of alkaline dehydrohalogenatingagents include, among others, the alkali metal hydroxides such as sodiumhydroxide, potassium hydroxide, etc., the alkaline earth metal oxidesand hydroxides such as calcium oxide, calcium hydroxide, etc., andvarious organic bases. Lime (calcium oxide) is a presently mostpreferred dehydrohalogenating agent.

Said dehydrohalogenation zone can comprise a stirred batch reactorprovided with a heating or cooling jacket through which a heat exchangemedium can be passed. Said stirred batch reactor represents onepreferred type of apparatus. It is ,within the scope of the invention touse two or more such reactors manifolded together for onolf operation,e.g., one or more vessels on stream while one or more other vessels arebeing recharged with dehydrohalogenating agent. It is within the scopeof the invention to employ other dehydrohalogenating means such aspacked columns lwherein a liquid dehydrohalogenating agent such as asolution of sodium hydroxide is passed countercurrently to a streambeing treated, or continuous or semicontinuous means wherein a solutionor other dispersion of the dehydrohalogenating agent is passedcountercurrent to the stream being treated.

The dehydrohalogenation reaction can be carried out under any reactionconditions of temperature, pressure, time, and using any amount ofdehydrohalogenating agent suitable for effecting the desireddehydrohalogenation.

The actual choice of said reaction conditions will depend upon, to alarge extent, the dehydrohalogenating agent being used and the materialsbeing treated. The temperature should not be great enough to causedehydrouorination. Generally speaking, the temperature can be within therange of about to 500 F. (43 to 260 C.). The pressure will be suiiicientto maintain the dehydrohalogenating agent in liquid or solid phase, andwill usually be within the range of from about 15 to about 680 p.s.i.a.It is preferred that the stream or material being treated be in thevapor phase. However, it is within the scope of the invention for saidmaterial being treated to be in the liquid phase. When lime (calciumoxide) is being used as the dehydrohalogenating agent, the preferredtemperature will usually be in the range of about 150 to 200 F. (66 to93 C.), and the pressure will be Within the range of about 50v to 150p.s.i.a.

The amount of dehydrohalogenating agent present in thedehydrohalogenation zone will be an amount which is at least sufcient toreact with the halogen acid being removed from the partially halogenatedfluorohydrocarbon impurity. For example, when said dehydrohalogenatingagent is lime, the stoichiometric amount is 0.5 mol of lime per mol ofhalogen acid being removed. Stated another Way, when chlorine is halogento be removed, the amount of lime required will be in the order of 0.8pound of lime per pound of chlorine to be removed. It is preferred touse an excess of lime in the dehydrohalogenation zone, e.g., up to about200, preferably 25 to 50, weight percent excess over the stoichiometricamount. Said lime can conveniently be charged to the reactor as anaqueous slurry containing from about to about 40, preferably from about15 to about 30, weight percent of lime. The contact time is not criticalbecause the reaction proceeds smoothly and rapidly to essentialcompletion with the formation of the corresponding olens. Depending uponthe efficiency of the contacting between the material being treated andthe dehydrohalogenating agent, the contact time will usually be in therange of from about 10 seconds to about 30 minutes.

An eluent stream comprising said corresponding olens and perhalogenatedfluorocarbons is withdrawn from dehydrohalogenation zone 56 via conduit60 and introduced into a third fractionation zone comprisingfractionation column 62. Said column 62 can conveniently be operated ata pressure of about 200 p.s.i.a., a top tower temperature of about 120F. (49 C.), and a bottom tower temperature of about 220 F. (104 C.). Anoverhead stream comprising said corresponding olefns is withdrawn fromsaid fractionation column 62 via conduit 64 and introduced intohalogenation zone 66. Said halogenation zone 66 can comprise anysuitable process and apparatus known to the art for halogenatinglluorinated hydrocarbons. For example, said halogenation zone cancomprise means for halogenating the fluorohydrocarbons thermally by themethods disclosed iny U.S. Pat. 2,644,845. Preferably, said halogenationzone will comprise means for photochemically halogenating saidfluorohydrocarbons using ultraviolet light by methods well known in theart. Said photochemical processes are usually caried out by contactingthe materialpto be halogenated with a halogen, e.g., chlorine, -ata-temperature within the range of from about -30 to 100 C., preferablyabout 10 to about 30 C., anda pressure sufficient to maintain thematerial being halogenated in liquid phase. However, any suitablereaction conditions, including vapor phase conditions, can be used inthe practice of the invention. Said halogenation reaction is-preferablycarried to completion. Further details of photochemicalV halogenationprocesses can be found in U.S. Pats. 3,494,844; 3,402,- 114; 3,296,108;3,019,175, and others. In some instances, it will be preferred to carryout the halogenation batchwise, or semibatchwise, so as to moreconveniently effect s ing column 70. A stream comprising partiallyhalogenated fluorohydrocarbons is withdrawn as a bottom stream fromfractionation column 70 via conduit 72. If desired, said stream inconduit 72 can be removed from the system via conduit 74. However, whenthe mixture of perhalogenated fluorocarbons and partially halogenatediluoro.- hydrocarbons being processed in accordance with the inventionis obtained as an effluent stream from an electrochemical lluorinationprocess, it is preferred that the stream in conduit 72 be passed intoconduit 76 for recycle via conduit 50 to said electrochemicaliluorination cell as a portion of the feedstock thereto.

An overhead stream comprising 1,l,2trichloro-1,2,2 triiluoroethane iswithdrawn from fractionation column 70 via conduit 78, and iscombinedwith a bottom stream comprising said trichlorotriuoroethane and1,2-dich1orotetrafluoroethane Withdrawn from fractionation column 62 viaconduit 80. The combined stream is then passed via conduit 82 into aifth fractionation zone comprising fractionation column 84 andfractionation column 94. Said fractionation column 84 can convenientlybe operated at a pressure of about 65 p.s.i.a., a top tower temperatureof about F. (49 C.), and a bottom tower temperature of about 215 F. (102lC.). An overhead stream comprising said 1,Z-dichlorotetrafluoroethaneis Withdrawn from fractionation column 84 via conduit 86 as a product ofthe process. A bottom stream comprising saidl,1,2-trichloro-1,2,2-triuoroethane is withdrawn from fractionationcolumn 84 via conduit 88. Said stream in conduit 88 will frequentlycontain some 1,2-dichloro- 1,2,2-trifluoroethane. In such instances, ifdesired, at least aportion thereof can be passed via conduit 90 intoconduit 50 for recycle to the electrochemical iluoriuation cell for thefurther production of said 1,2-dichlorotetrauoroethane. In mostinstances, and particularly when it is desired to produce the maximumamount of said 1,1,2- trichloro-1,2,2-trifluoroethane said stream inconduit 88 will preferably be passed via conduit 92 into fractionationcolumn 94. Said fractionation column 94 can conveniently be operated ata pressure of about 30 p.s.i.a., a top tower temperature of about 123 F.(51 C.), and a bottom tower temperature of about F. (71 C.). An overheadstream comprising said 1,2-dichloro-1,2,2-triiluoroethane is withdrawnfrom fractionationcolumn 94 via conduit 96 and removed from the system.If desired, said stream in conduit 96 can be passed via conduit 98 intoconduit 99 for introduction into conduit 50 for recycle to theelectrochemical fluorination cell. A bottom stream comprising said 1,1,2trichloro 1,2,2 trifluoroethane is withdrawn from fractionation column94 via conduit 100 as a major product of the process.

The following calculated example will serve to further illustrate theinvention. The conditions set forth for the operation of theelectrochemical uor'ination cell are based upon numerous laboratory andpilot plant runs carried out for the electrochemical fluorination of1,2- dichloroethane.

EXAMPLE In this illustrative embodiment a run is carried out for theelectrochemical uorination of 1,2-dichloroethane in a system embodyingthe essential features of the system illustra-ted in the drawing andusing an electrolyte in cell 10 which has an approximate composition ofKF'2I-H?. Porous carbon cylinders embodying the essential features ofanode 14 illustrated diagrammatically in the drawing are employed asanodes.,Fresh 1,2-dichlorocthane feedstock is introduced via conduits26and 28 into the pores of anode 14. Recycle feedstock is supplied byconduit 50. The conversion in electrolytic cell 10 is carried out at anelectrolyte temperature of about-210 F, (99 0.), employing a currentdensity of about 250 amperes per square foot of anode geometric surfacearea, and a voltage of about 9.5 volts, D.C. The pressure in cell 10,and conduit 30, is substantially atmospheric. A cell eflluent stream iswithdrawn via conduit and processed in zone 32 for the removal ofhydrogen and HF, and the return of a recycle stream of HF via conduit33. Hydrogen is removed from the system via conduit 35. Table I belowsets forth the principal components in said cell elluent stream and theprincipal components in the other major streams of the system, and acalculated material balance for the system.

10 dustry. In the separation of mixture such as that set forth in feedstream 34 by fractional distillation, the recovery of the product1,Z-dichlorotetrauoroethane is favored with the ratio of recovered saidtrichlorotriuoroethane product to recovered said dichlorotetrauoroethaneproduct being approximately 0.6. In the practice of this invention theratio of recovered said trichlorotriuoroethane product to recovered saiddichlorotetrailuoroethane product from said stream 34 is approximately1.6. Both of said TABLE I Stream number, mols per hour Components 34 4244 52 46 60 64 80 68 78 72 86 92 96 100 CCIFFCCW, 16.3 0.8 15.5 15.555.5 15.5 CHClFCC1Fq. 14.7 14.7 14.7 0.66 0.86 0 66 0.66 CClFa-CHZCL.-5.4 .4 5.4 0.66 0.06 0.60 0 0.06 CHClF-CHCIF .8 2.0 7.8 CHClF-CHlCl-- .70.2 14.5 CHaCl-CHzCl .3 24.3

lFresh feedstock to cell.

From the data set forth in Table I above, it can be readily seen thatthe production of 1,l,2-trichloro-1,2,2 trifluoroethane is markedlyincreased in the practice of the invention, even on a once-throughbasis. For example, referring to feed stream 34 in Table I, it will benoted that said stream 34 contains l0 moles per hour of 1,l,2-tricholo-1,2,2-triliuoroethane. Product stream 100 contains 24.45 molsper hour of said trichlorotrifluoroethane product. This increase in theproduction of said trichlorotriuoroethane product is due largely to theconversion of 1,2-dichloro-1,2,2-trifluoroethane which, in the practiceof this invention, is converted to said 1,1,2trichloro-1,2,2triuoroethane product. Said l,2-dichloro-1,2,2triiluoro ethane isconverted in dehydrohalogenation zone 56 t0l-chloro-1,2,2-triuoroethylene, which in turn is converted to saidtrichlorotriuoroethane product in chlorination zone 66, which product isultimately recovered via conduit 100. It will also be noted that saidtrichlorotriuoroethane product recovered in conduit 100 is a high purityproduct. Said trichlorotrifluoro product has a boiling point of 47.6 C.Another fluorinated material which is usually present in mixturestreated in accordance with this invention,1,2-dichloro-1,l-diuoroethane, has a boiling point of 46.8 C. This makesthe recovery of said trichlorotriuoroethane product by fractionaldistillation very dilicult and very expensive from a practical operatingstandpoint. This ditiicult separation is avoided in the practice of thepresent invention because said l,2dichloro 1,1-difluoroethane isconverted in dehydrohalogenation zone 56 to 1chloro-2,2diuoroethylene,which in turn is then converted to l,2,2-trichloro1,1-difluoroethane inhalogenation zone 66. This last-mentioned material has a boiling pointof 71.9 C., lthus eliminating the abovereferred-to dicnlt fractionationproblem.

Said l,1,2-trichloro-1,2,2-trifluoroethane is a'valuable product havingutility as a refrigerant, and particularly valuable utility as acleaning solvent in the aerospace inproducts can be employed asrefrigerants. However, due to its lower volatility, saidtrichlorotriuoroethane product, having a boiling point of 47.6 C.compared to a boiling point of only 3.6" C. for said dichlorotetrauoroproduct, is preferred for a cleaning solvent. The increased amount ofsaid trichlorotrilluoro product is an important consideration when oneis interested in producing said product for the cleaning solvent market.

While certain embodiments of the invention have been described forillustrative purposes, the invention is not limited thereto. Variousother modifications or embodiments of the invention will be apparent tokthose skilled in the art in view of this disclosure. Such modificationsor embodiments are Within the spirit and scope of the disclosure.

I claim:

1. In a process for the separation of, and the recovery of, saturatedperhalogenated acyclic fluorocarbons contained in a mixture withsaturated halogenated acyclic lluorohydrocarbons which contain a halogenother than uorine and at least some of which are capable of beingdehydrohalogenated to the corresponding olefin, which process comprises,in combination, the steps of:

(a) contacting said mixture in a dehydrohalogenation zone with adehydrohalogenation agent and dehydro halogenating said halogenatediluorohydrocarbon compounds to remove therefrom a-t least one atom ofhydrogen and one atom of said halogen other than uorine and produce asecond mixture contain--4 ing -said corresponding olens; and

(b) fractionating an eiuent stream from said dehydrohalogenation zone torecover an overhead stream comprising said olefins, and a bottoms streamcornprising said perhalogenated uorocarbons; the irnprovement comprising(c) passing said overhead stream from step (b) to a halogenation zoneand therein halogenating said olens to perhalogenated uorocarbons;

(d) fractionating an eluent stream from said halogenation zone torecover an over-head stream comprising said perhalogenated uorocarbonproduced in said step (c);

(e) combining said bottoms stream from step (b) and said overhead streamfrom step (d) to obtain a second mixture comprising said perhalogenatedfluorocarbons present in said rst'mixture and said perhalogenatediluorocarbon produced in said step (c); and

(f) fractionating said second mixture to separate and recover saidperhalogenated uorocarbons.

2. A process according to claim 1 wherein said halogen other than uorineis chlorine.

3. A process according to claim 1 wherein:

said rst-mentioned mixture comprises perhalogenated uorocarbonsincluding 1,2-dich1orotetrauoroethane and1,1,2-trich1oro-1,2,2-triuoroethane; and partially halogenatedfluorohydrocarbons includingl 1,2-dichloro-1,2,2-trifluoroethane,1,2-dichloro-1,ldiiiuoroethane, and 1,2-dichloro-l,2-dif1uoroethane;said overhead stream recovered in step (b) comprises1-chloro-1,2,2-diuoroethylene, 1-chlor0-2,2diuoroethylene, andl-chloro-1,2-diuoroethylene; said bottoms stream recovered in step (b)comprises 1,2-dichlorotetrauoroethane and 1, 1,2-trichloro-1,2,2-trifluoroeth ane;

said overhead stream recovered in step (d) comprises1,1,2-trichloro-1,2,2-triuoroethane; and

said second mixture of step (e) is fractionated in step (f) to recover1,2-dichlorotetrauoroethane as one perhalogenated uorocarbon product ofthe process, and 1,1,2 triuoro-l,2,2-triiluoroethane as anotherperhalogenated uorocarbon product of the process.

4. A process according to claim 3 wherein said firstmentioned mixturealso contains chloropentauoroethane and, prior to step (a), said mixtureis fractionated to recover a stream comprising saidchloropentauoroethane as another product of the process.

5. A process according to claim 1 wherein said perhalo- 4genateduorocarbons and said partially halogenated uorohydrocarbons each containfrom 2 to 4 carbon atoms per molecule.

6. A process according to claim S wherein said perhalogenateduorocarbons and said partially halogenated uorohydrocarbons each contain2 carbon atoms per molecule.

7. In a process for the uorination of a halogenated hydrocarbonfeedstock wherein there is produced a mixture of saturatedperhalogenated acyclic uorocarbons containing a halogen other thanfluorine and partially halogenated saturated acyclic uorohydrocarbonsalso containing said halogen other than iluorine, and wherein saidperhalogenated uorocarbons are recovered from said mixture, by Y (a)passing at least a portion of said mixture to a dehydrohalogenation zoneand therein dehydrohalogenating said partially halogenatedtluorohydrocarbons to remove therefrom at least one atom of hydrogen andone atom of said halogen other than uorine and produce a second mixturecontaining corresponding olens; and

(b)lfractionating an eiuent stream from said dehydrohalogenationzone torecover Van overhead stream comprising said olens, and a bottoms streamcomprising perhalogenated iluorocarbons; the improvement comprising p(c) passing said overhead stream from step (b) to a halogenation zoneand therein halogenating said olens to perhalogenated uorocarbons;

(d) fractionating an eflluent stream from said halogenation zone torecover an overhead stream comprising said perhalogenated uorocarbonsproduced in said Step (6);

(e) combining said bottoms stream from step (b) and said overhead streamfrom step (d) to obtain a second mixture comprising said perhalogenateduorocarbons present in said first-mentioned mixture and saidperhalogenated uorocarbons produced in step (6); and

(f) fractionating said second mixture to separate and recover saidperhalogenated uorocarbons.

References Cited UNITED STATES PATENTS 2/ 1953 Miller 260-653.5 7/ 1959Prill 260-653.5 8/ 1965 Sianesi et al 26o-653.5 5/ 1969 Hutton 260-653.53/19'54 Ruh 260-653.5 4/ 1954 Skiles 260-653.5

